阅读说明：本技术 一种镁掺杂二硫化钴复合碳纳米管材料、制备方法与应用 (Magnesium-doped cobalt disulfide composite carbon nanotube material, preparation method and application ) 是由 乔锦丽 郭佳宁 徐能能 王旭 王永霞 娄文双 李君� 于 2020-07-07 设计创作，主要内容包括：本发明公开了一种镁掺杂二硫化钴复合碳纳米管材料、制备方法与其在制备锌空电池阴极催化剂中的应用。制备方法为采用了水热法制备具有氧还原和氧析出反应的锌空电池阴极催化剂,即使用硝酸镁作为掺杂剂,醋酸钴作为钴基金属硫化物原料,硫粉作为硫化剂,将金属硫化物和碳纳米管通过惰性气氛下高温复合。该方法在金属和碳材料的结合作用下,一方面可以有效抑制钴的团聚,另一方面在碳纳米管上同步生成了具有高效催化氧还原的氧空穴以及具有析氧活性的二硫化钴微粒,最终得到的催化剂材料用在锌空电池上可实现长时间,高稳定性的充放电循环。(The invention discloses a magnesium-doped cobalt disulfide composite carbon nanotube material, a preparation method and application thereof in preparation of a zinc-air battery cathode catalyst. The preparation method adopts a hydrothermal method to prepare the zinc-air battery cathode catalyst with oxygen reduction and oxygen precipitation reactions, namely magnesium nitrate is used as a doping agent, cobalt acetate is used as a cobalt-based metal sulfide raw material, sulfur powder is used as a vulcanizing agent, and the metal sulfide and the carbon nano tube are compounded at a high temperature in an inert atmosphere. Under the combined action of metal and carbon materials, the method can effectively inhibit cobalt agglomeration on one hand, and synchronously generate oxygen cavities with efficient catalytic oxygen reduction and cobalt disulfide particles with oxygen evolution activity on the other hand, and the finally obtained catalyst material can realize long-time and high-stability charge-discharge circulation when used on a zinc-air battery.)

1. A preparation method of a magnesium-doped cobalt disulfide composite carbon nanotube material is characterized by comprising the following steps:

step 1): mixing with Co (Ac)₂·4H₂O and Mg (NO)₃)₂·6H₂Adding O into deionized water, stirring until crystals disappear, and then transferring to an ultrasonic machine for ultrasonic oscillation to ensure complete dissolution;

step 2): adding carbon nanotubes into the solution obtained in the step 1), and performing ultrasonic stirring to obtain a mixed solution;

step 3): transferring the mixed solution obtained in the step 2) to a stirrer, and adding a dispersing agent under magnetic stirring;

step 4): ultrasonically oscillating the mixed solution obtained in the step 3), transferring the mixed solution into a polytetrafluoroethylene lining of a reaction kettle, and putting the polytetrafluoroethylene lining into a blast drying oven for hydrothermal drying;

step 5): taking out the mixed solution after the hydrothermal drying, pouring out the supernatant, centrifuging, washing with water and alcohol for three times respectively, and transferring to an air-blast drying oven for drying;

step 6): collecting the dried precipitate, grinding the dried precipitate into fine powder by using a mortar, transferring the fine powder into a tube furnace for calcining, naturally cooling to room temperature, and collecting to obtain the magnesium-doped cobalt disulfide composite carbon nanotube.

2. The method for preparing the magnesium-doped cobalt disulfide composite carbon nanotube material of claim 1, wherein Co (Ac) in the step 1)₂·4H₂O and Mg (NO)₃)₂·6H₂The molar ratio of O is 2: 1.

3. The method for preparing the magnesium-doped cobalt disulfide composite carbon nanotube material of claim 1, wherein the mass of the carbon nanotubes in the step 2) is 50mg, and the particle diameter is 20-30 nm.

4. The method for preparing the magnesium-doped cobalt disulfide composite carbon nanotube material of claim 1, wherein the dispersant in the step 3) adopts sulfur powder and ethanol, wherein the mass ratio of the sulfur powder to the mixed solution is 0.64g, and the volume ratio of the ethanol to the mixed solution is 5-8 mL.

5. The method for preparing the magnesium-doped cobalt disulfide composite carbon nanotube material according to claim 1, wherein the hydrothermal temperature of the forced air drying oven in the step 4) is set to 160 ℃ and the time is set to 6 hours.

6. The method for preparing the magnesium-doped cobalt disulfide composite carbon nanotube material of claim 1, wherein nitrogen is pre-introduced for 45min under the condition of nitrogen before the tubular furnace in the step 6) is calcined, the temperature is increased to 350 ℃ at the speed of 5 ℃/min, and the temperature is maintained for 1 h.

7. The magnesium-doped cobalt disulfide composite carbon nanotube material prepared by the preparation method of the magnesium-doped cobalt disulfide composite carbon nanotube material of any one of claims 1 to 6.

8. The magnesium-doped cobalt disulfide composite carbon nanotube material of claim 7, wherein the material is a cobalt-based sulfide in-situ supported carbon nanotube material with a specification of 50-100nm, and the cobalt-based sulfide has oxygen evolution/hydrogen evolution catalytic activity.

9. The use of the magnesium-doped cobalt disulfide composite carbon nanotube material of claim 7 or 8 in the preparation of a zinc-air battery cathode catalyst.

Technical Field

The invention relates to a regulated and synthesized magnesium-doped cobalt disulfide composite carbon nanotube material, a preparation method and application, and belongs to the technical field of oxygen electrochemical reduction/precipitation bifunctional catalysts.

Background

At present, fossil energy loss and environmental pollution are increasingly aggravated, and environmental problems such as energy urgency and greenhouse effect caused by the aggravation make the development of novel sustainable energy storage devices difficult. From the application perspective of many energy systems, batteries represent a promising and viable energy conversion technology. Among them, electrochemical energy sources represented by rechargeable zinc-air batteries (ZABs) have attracted much attention because of their advantages of low cost, environmental friendliness, high safety, high energy density, and the like. The theoretical energy density of the zinc-air battery is 1218Wh kg^-1About 4 times of that of the lithium ion battery, rich metal zinc reserves, low price and safe control in an aqueous solution (KOH) electrolyte system. However, the most important factor hindering the development of the zinc-air battery is the development and utilization of a cathode catalyst (air electrode). On the cathode side, the cell discharge/charge process manifests itself as oxygen reduction and evolution reactions (ORR/OER), respectively, which also determine the energy efficiency and cycle life of the cell. Slow kinetics of ORR and OER multiple interfaces delay the development of ZABs and O ═ O bond energy (498kJ · mol) during charging and discharging^-1) Also requires more energy (higher overpotential). In order to overcome the above problems, noble metals of platinum (Pt), ruthenium (Ru), iridium (Ir) and oxides thereof are still widely used commercial catalysts. However, although these precious metal catalytic materials have high ORR and OER activities, their high cost, scarce storage and poor stability severely hinderThe scale development of the method is improved. Therefore, reasonably constructing a low-cost, high-activity and high-stability bifunctional oxygen electrode which is beneficial to structure and appearance optimization becomes a focus and a hot spot of current research.

Transition metal compounds have attracted much attention because of their excellent oxygen catalytic properties, and among them, transition metal oxides, transition metal nitrides, and the like have been widely studied because of their advantages such as charge-discharge stability, small resistance, and the like. Among these transition metal oxides, metal cobalt-based spinel catalysts have been attracting attention due to their special physical and chemical structures. In particular, the activity of cobalt-based metal oxide catalysts can be modulated by the composition of the ions, such as MnCo₂O₄，NiCo₂O₄And CoO_0.87S_0.13. The stability and activity of these cobalt-based transition metal oxide catalysts is still limited by their undesirable chemical structure, the instability of which is mainly due to surface cation segregation, impurities and phase precipitation. The chemical stability of the catalyst is improved effectively by regulating and controlling the chemical properties of the catalyst. In view of the extensive research on transition metal oxide catalysts, there are few reports of research on designing the intrinsic properties and improving the electrocatalytic performance of oxides by synergistically engineering their anionic chemistry and cationic chemistry. Compared with the commonly used iron-cobalt-nickel ions, the hydroxyl coordination capacity of the magnesium ions is weaker, and more catalytic buffer interfaces with weak lattice basicity can be formed. In addition, sulfur (S) and oxygen (O) both belong to oxygen group (VIA), and transition metal sulfides can maintain the crystal morphology and activity of the transition metal oxide catalyst while generating different distorted structures and more abundant oxygen vacancies. In order to improve the electron conductivity of the catalyst system, it is necessary to introduce a carbon-based additive as a conductive agent. In previous studies, carbon nanotubes have effectively improved the stability and conductivity of oxide and sulfide catalysts due to their high conductivity, high electrochemical stability, and large surface area. Therefore, the research on the controllable occupation of S, Mg ions in the carbon-supported transition metal sulfide bifunctional catalyst is of great significance for improving the catalytic activity and stability of the carbon-supported transition metal sulfide bifunctional catalyst.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a magnesium-doped cobalt disulfide composite carbon nanotube ((Co, Mg) S) with bifunctional activity₂@ CNTs).

In order to solve the technical problem, the invention provides a magnesium-doped cobalt disulfide composite carbon nanotube material ((Co, Mg) S)₂@ CNTs) preparation method, characterized by comprising the following steps:

step 1): mixing with Co (Ac)₂·4H₂O and Mg (NO)₃)₂·6H₂Adding O into deionized water, stirring until crystals disappear, and then transferring to an ultrasonic machine for ultrasonic oscillation to ensure complete dissolution;

step 2): adding carbon nanotubes into the solution obtained in the step 1), and performing ultrasonic stirring to obtain a mixed solution;

step 3): transferring the mixed solution obtained in the step 2) to a stirrer, and adding a dispersing agent under magnetic stirring;

step 4): ultrasonically oscillating the mixed solution obtained in the step 3), transferring the mixed solution into a polytetrafluoroethylene lining of a reaction kettle, and putting the polytetrafluoroethylene lining into a blast drying oven for hydrothermal drying;

step 5): taking out the mixed solution after the hydrothermal drying, pouring out the supernatant, centrifuging, washing with water and alcohol for three times respectively, and transferring to an air-blast drying oven for drying;

step 6): collecting the dried precipitate, grinding into fine powder with a mortar, transferring into a tube furnace for calcining, naturally cooling to room temperature, and collecting to obtain the magnesium-doped cobalt disulfide composite carbon nanotube ((Co, Mg) S₂@CNTs)。

Preferably, the Co (Ac) in the step 1)₂·4H₂O and Mg (NO)₃)₂·6H₂The molar ratio of O is 2: 1.

Preferably, the mass of the carbon nanotubes in the step 2) is 50mg, and the particle diameter is 20-30 nm.

Preferably, the dispersant in step 3) is sulfur powder and ethanol, wherein the mass ratio of the sulfur powder to the mixed solution is 0.64g, and the volume ratio of the ethanol to the mixed solution is 5-8 mL.

Preferably, the hydrothermal temperature of the forced air drying oven in the step 4) is set to be 160 ℃ and the time is set to be 6 hours.

Preferably, nitrogen is introduced into the tube furnace for 45min under the condition of nitrogen before the tube furnace in the step 6) is calcined, the temperature is increased to 350 ℃ at the speed of 5 ℃/min, and the temperature is kept for 1 h.

The invention also provides the magnesium-doped cobalt disulfide composite carbon nanotube material prepared by the preparation method of the magnesium-doped cobalt disulfide composite carbon nanotube material.

Preferably, the material is a carbon nanotube material loaded with a cobalt-based sulfide in situ, the specification of which is 50-100nm, and the cobalt-based sulfide has oxygen evolution/hydrogen evolution catalytic activity.

The invention also provides application of the magnesium-doped cobalt disulfide composite carbon nanotube material in preparation of a cathode catalyst of a zinc-air battery.

The invention forms double active sites on the surface of the carbon nano tube material to synchronously improve the electrocatalytic oxygen reduction and oxygen evolution capability of the composite material by carrying out negative magnesium doping on the cobalt disulfide particles.

Compared with the prior art, the invention has the following beneficial effects:

(1) the invention adopts a simple hydrothermal crystallization method to synthesize (Co, Mg) S applicable to the rechargeable zinc-air battery₂@ CNTs bifunctional electrocatalysts. The preparation method is green and environment-friendly, compared with the traditional metal sulfide, the method has no complicated steps, and only uses 350 ℃ for calcination, thereby avoiding high energy consumption. Passing through a low concentration (< 0.2%) of Mg²⁺And the crystal and the appearance of the hybrid catalyst can be effectively adjusted by doping. The catalyst has high preparation repeatability and low cost, and can be prepared in a large scale.

(2) Aiming at the characteristic that metal sulfide particles are easy to agglomerate, the invention skillfully enables cobalt disulfide particles to grow on the carbon nano tube in situ, effectively inhibits the agglomeration of cobalt, forms nano cobalt sulfide particles with small particle size (50-100nm), and simultaneously enables the particle size and elements to be uniformly distributed by doping magnesium, thereby avoiding the defect of poor performance.

(3) The invention is inMagnesium salt is added in the preparation process of the composite material, so that the formation of cobalt disulfide in the hydrothermal process is promoted to be more stable, and more oxygen reduction active sites are formed. Thus prepared magnesium-doped cobalt disulfide composite carbon nano-tube ((Co, Mg) S)₂@ CNTs) has excellent bifunctional characteristics, and exhibits high stability and cycle performance when applied to zinc-air batteries.

(4) The synthesized magnesium-doped cobalt disulfide composite carbon nanotube material can realize long-time constant-current discharge when being used for a disposable zinc-air battery, and can continuously discharge for more than 70 hours at a current density of 10 milliamperes; can realize charge and discharge cycle for a very long time, can still stably run after 300 charge and discharge cycles are realized, and has high peak power density (268mW cm)^-2) Provides a good foundation for the practical industrial application of the battery.

Drawings

FIG. 1 shows bifunctional (Co, Mg) S₂A synthesis and preparation flow chart of @ CNTs;

FIG. 2a shows (Co, Mg) S prepared in example 3₂SEM picture of @ CNTs;

FIG. 2b is a SEM image of the carbon nanotubes after the same treatment;

FIG. 2c shows (Co, Mg) S prepared in example 3₂TEM image of @ CNTs;

FIG. 2d shows (Co, Mg) S prepared in example 3₂The active site crystal face schematic diagram of @ CNTs;

FIG. 2e shows (Co, Mg) S prepared in example 3₂The EDS diagram for @ CNTs;

FIG. 3a shows (Co, Mg) S prepared in example 5₂@ CNTs catalyst and commercial Pt/C-RuO₂A power comparison plot for the catalyst;

FIG. 3b shows (Co, Mg) S prepared in example 5₂@ CNTs and Pt/C-RuO₂Graph comparing 10ma discharge;

FIG. 3c shows (Co, Mg) S prepared in example 5₂@ CNTs and Pt/C-RuO₂5 milliampere charging and discharging comparison graph;

FIG. 3d is (Co, Mg) S prepared in example 5₂@ CNTs 50 milliamp charge-discharge performance plot.

Detailed Description

In order to make the invention more comprehensible, preferred embodiments are described in detail below with reference to the accompanying drawings.

And (3) performance measurement: the microscopic morphology of the products of the examples of the invention was tested by TEM (JEOL JEM-2100F system), SEM (Hitachi S-4800) and elemental analysis was determined by XPS (RBDupgrad PHIE5000C ECSA system (Perkinelmer)). Half-cell performance testing was performed using a three-electrode system on the Chenghua CHI760D electrochemical workstation. Single cell testing was performed on a CT2001A blue cell testing system.